Fix mutate-changes failing on pull_request CI events#466
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On pull_request events the *-mutate workflows set GIT_BASE_SHA to ''. Make's `?=` does not override an env var that is already defined (even when empty), so `mutant run --since` was invoked with no base ref, and mutant's git-diff bootstrap blew up with Mutant::Repository::Diff::Error. - Workflows: use github.event.pull_request.base.sha on PRs instead of '' (full history is already available via fetch-depth: 0). - Makefiles: compute merge-base when GIT_BASE_SHA is set-but-empty via $(or ...), so a blank env can never reach mutant again. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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A push of a new branch sets github.event.before to the all-zero git SHA (0000…0), which is non-empty so it slipped past the $(or ...) guard and was passed to `mutant --since`, failing the same way an empty value did. Filter out the null SHA too, so both an empty and a null base fall back to `git merge-base HEAD origin/master` (diff the branch against master). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Fix mutate-changes failing on pull_request CI events
Problem
The pricing-mutate and rails_application-mutate workflows fail on every PR
during mutant bootstrap:
Running incremental mutation tests against ... ← GIT_BASE_SHA is empty
Mutant::Repository::Diff#touched_path: ...CommandStatus...
(Mutant::Repository::Diff::Error)
Root cause
Both workflows set the base SHA like this:
GIT_BASE_SHA: ${{ github.event_name == 'push' && github.event.before || '' }}
On a pull_request event the ternary resolves to ''. The Makefiles default it
with:
GIT_BASE_SHA ?= $(shell git merge-base HEAD origin/master)
but ?= only assigns when the variable is undefined — an env var exported as an
empty string still counts as defined, so the merge-base fallback never runs.
mutant run --since is then invoked with no base ref, and mutant's git-diff
bootstrap raises Mutant::Repository::Diff::Error. This hits every PR (the
workflows trigger on pull_request: [opened, reopened] with no path filter),
independent of what the PR changes.
Fix
github.event.pull_request.base.sha instead of ''. Full history is already
available via fetch-depth: 0, so the base commit is present for --since.
the merge-base when GIT_BASE_SHA is set-but-empty using $(or
never reach mutant again (defense in depth, also helps local runs).
Scope
CI-only change, 4 files, 4 lines. No application code touched.
🤖 Generated with Claude Code